Method and apparatus for separating magnetic from nonmagnetic materials



y 4, 1949, A. B. DRESCHER 2,470,889

METHOD AND APPARATUS FOR SEPARATING MAGNETIC FRGM NONMAGNETIC MATERIALS Filed oat. 5, 1944 2 Sheets-Sheet 1 Arth ur B. Drescher QMW May 24, 1949. A. B. DRESCHER 7 METHOD AND APPARATUS FOR SEPARATING MAGNETIC FROM NONMAGNETIC MATERIALS Filed Oct. 5, 1944 2 Sheets-Sheet 2' V p r i w s? 5 a Arthur B. breach or Patented May 24, 1949 METHOD AND APPARATUS FOR SEPARAT- IN G MAgNETIC FROM NONMAGNETIC MA- TERIAL Arthur B. Drescher, Daingerfield, Tex., assignor to Lone Star Steel Company, Daingerfield, Tex,

Application October 5, 1944, Serial No. 557,314

This invention relates to new and useful improvements in methods and apparatus for separating magnetic from non-magnetic materials. As is well-known, the majority of magnetic separators are of the direct-current type which are ineificient in obtaining concentrates from fine ore uncontaminated by free gangue. This is due to the fact that, upon use of a magnetic (directcurrent) field of sufficient intensity, the magnetic particles are attracted to each other as well as to the magnetic field. Thus, some of the nonmagnetic waste material or gangue is inevitably entrained by the mutually-attracted magneti particles. Magnetic separators utilizing a series of alternate North and South, or positive and negative, poles are also inefficient, because the speed of passage of the ore particles through such alternate fields is not suflicient to permit hysteretic repulsion and attraction. As the ore particles pass from, one pole to another of op posite sign, said particles merely turn end for end, often in groups with physically-entrapped gangue therein, and without actually being repulsed.

or sloping surface along which the active, or activated, particles progress downwardly by gravity, an absolutely clear out or definite separation is impossible. Due to the violent motion of the magnetic particles, a considerable quantity of the middlings as Well as some of the free gangue or quartz is so physically agitated that the same progress down the inclined surface to contaminate the concentrates.

Although an alternating current magnetic field has been employed heretofore in magnetic separators, the same has been used as a .repulsion magnet and has been located beneath the stream or path of the ore particles so as to have its force directed from underneath said particles. In this type of separation, the theory of operation is that the magnetic material and waste will be stratified with said magnetic material working to, or accumulating at, the top ofthe bed whereby the concentrates will be removed or separated out upon being subsequently passed through a direct-current magnetic field; The main disadvantage of this type'of separation is that perfect stratification is unobtainable, since middlings and some free gangue will become admixed with the concentrates due to the rather Violent agitation, especially when the material settles back to the bed upon passing from the alternating-current magnetic field. Thus, the

4 Claims. (Cl. 209214) 2. stratified condition of the particles is at least partially lost by the time the same reaches the direct-current magnetic field. The altematingcurrent magnetic field merely prepares the particles for the actual separation step-by the direct-current magnetic field and does nothave any part in accomplishing such separation.

Combined direct-current and alternating-current attracting magnets have been utilized in separators in which the separation takes place under water. However, the water dampens the activity'of the particles in the alternating-cur- I rent magnetic field so as to reduce or impede the In magnetic separators utilizing an inclined efiectiveness of the separation. Not only does the resistance of the water retard the motion of the magnetic particles, but 'it also prevents the gangue from draining or dropping out as rapidly as is desirable and as it would in the free atmosphere. Manifestly, these factors limit the recovery and quality of the concentrates as well as the capacity of the separator.

By the use of nalternating-current magnetic field in a free or normal atmosphere for attracting the ore particles, the entrainment of gangue is almost entirely eliminated. Individual particles are attracted and repulsed alternately and, in general, each particle behaves or reacts more or less independently, as controlled by the direction of the magnetic field, the positions of the particles and other conditions. Thus, there is little chance for physical entrapment of waste material. During one half of the cycle, on the average, magnetic particles are repelled in an alternating current field, but are again attracted almost immediately during the other ha]! of the cycle, thereby keeping the particles in constant activity or motion. 'The response of a particle at any particular moment is the result of various conditions, suchas 'the' orientation of the magnetic poles of the particle, the shape of said particle, its freedom from crowding by adjacent particles, its locked condition (admixture with gangue), the direction of the magnetic field at the moment, etc. The composite or total effect of these variables results in attraction of'each magnetic particle during half of the cycle and repulsion thereof during the remaining half.

Therefore, one object of the invention is to provide improved means for magnetically separating materials having, or to which may be imparted, a relatively-high coercive force and a sllfi'lciently high remanence, which means effectively overcomes the inherent drawbacks of di-' "rect-current magnetic separatorsand, at the same time, more eflicient'ly utilizes the activity setup by an alternating-current field so as to obtain higher-grade concentrates as well as increased recoveries and capacities.

A particular object of the invention is to provide improved magnetic separation means having an alternating-current magnet through the field of which the ore, or other material to be separated, is conducted for initial activation which results in a preliminary segregation or separation of the active concentrates and inert tailings, said activated ore stream being subjected to the held of an alternating-current attracting magnet which physically separates said active concentrates from said inert tailings.

Another object of the invention is to provide improved magnetic separation means, of the character described, wherein the ore, or other material, is reduced in size to give the desired degree of liberation and, if necessary, properly con-' verted to a substance of sufliciently high coercive force and remanence; said ore being passed through the field of a direct-current magnet so as to be magnetized and subsequently activated and/or repulsed by the first alternating-current magnet and separated by the alternating-current "attracting magnet.

A further object of the invention is to provide an improved magnetic separator, of the character described, wherein a thin bed of dry ore is fed through the fields of the direct-current magnet and the activation and/ or repulsion magnet by suitable conveying means disposed above said magnets, the attracting magnet being of greater intensity than said repulsion magnet and having concentrate conveying means associated therewith, whereby the active concentrates will be activated and segregated from the inert tailings upon the feed-conveying means by said repulsion magnet and will be transferred to and further activated along the concentrate conveying means by said attracting magnet so as to be in a state of suspension and thereby release entrained tailings as well as middlings.

Still another object of the invention is to provide an improved magnetic separator, of the character described, wherein the attracting magnet and concentrate-conveying means are adjustably moimted so as to permit varying of the intensity of the effect of the magnet upon the magnetic particles of the material being separated; thm'e being means for mechanically agitating the material while the same is upon the feed-conveying means so as to permit the feeding of a thicker bed or stream of material.

An important object of the invention is to provide an improved magnetic separation method wherein the ore, or other material to be separated, is subjected to an alternating-current magnetic field of insuflicient strength to demagnetize the magnetic particles of the material whereby said particles are activated and segregated or separated from the inert tailings, said material then being subjected to and attracted by an alternating-mirrent magnetic field of greater intensity which physically removes or separates said magnetic particles from said inert tailings and suspends the same in a tenuous active mass so as to drop out entrained gangue or tailings.

Another object of the inve ntion'is to provide an improved method of magnetically separating materials, of the character described, wherein the intensity of the attracting magnetic field is not in excess of the coercive force of some of the magnetized particles, whereby saidparticles will mahitain their respective polarity and will adjust themselves by motion to the altematingcurrent, the activity of these particles causing the same to collide with particles having less coercive force so as to agitate the same and cause draining out of entrained gangue.

A construction designed to carry out the "invention will be hereinafter described together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and reference to the accompanying drawing, wherein 'an example of the invention is shown, and

wherein:

Fig. 1 is an isometric view of a magnetic separator constructed in accordance with the invention,

Fig. 2 is a plan view of the separator,

Fig. 3 is. an enlarged, transverse, vertical, sectional view,'taken on the line 3-3 of Fig. 2,

Fig. 4 is an enlarged, longitudinal, vertical, sectional view, taken on the line 44 of Fig. 2, and

Fig. 5 is an enlarged, isometric view of the nonmagnetic rake.

In the drawings, the numeral ll! designates the frame of a magnetic separator which is substan tially rectangular in cross-section and which includes a plurality of upright supporting legs or standards ll. Longitudinal beams l2 and transverse cross-heads or members l3 connect the upper ends of the legs II to each other, while each pair of end legs have their lower ends joined and reinforced by a suitable transverse foot member or plate l4. Below each beam l2 and in parallel, vertical alinement therewith, a reinforcing beam I5 extends longitudinally betweem and connects each pair of longitudinal legs. A suitable feed hopper I 6, preferably of the type capable of maintaining a steady and uniform, thin-bedded feed, such as an electromagneticallyvibrating type, is secured to one of the crossheads l3 and has its lower portion depending between and below the upper beams l2 adjacent one end of the separator frame Ill. The hopper has a constricted feed slot ll formed in its lower end, which slot terminates some distance above the beams f5.

As is clearly shown in Figs. 1 and 4, an endless conveyor or feed belt l8, of rubber or other suitable material, is disposed between the reinforcing beams I5 and is mounted upon suitable pulleys l9 and 20. The pulley I9 is of conventional construction and is supported by having its shaft 2| journaled in suitable brackets 22 which are fastened by bolts and nuts to the inner longitudinal surfaces of the legs it below the hopper l6. It is preferable that the pulley 20 be .constructed of wood or other non-magnetic material, and has its shaft 24 journaled in suitable brackets 25 which are secured to the upper surfaces of the beams l5 at their intermediate portions. Due to the disposition of the pulleys I9 and 20. the feed belt l8 extends throu hout slightly more than one-half the length of the separator frame l0 and said belt is of a width slightly greater than the length of the hopper feed slot l1 and slightly less than the distance between the beams [5 (Figs. 2 and 4). Also, the

upper flight of the belt is disposed immediately below the feed slot I! which, in turn. is positioned a slight distance forwardly of the pulley I9, whereby the dry ore, or other material to be separated, is fed from the hopper l6 through said feed slot directly upon said belt in a thin stream or bed. For driving the belt to the right 0 or in a clock-wise direction, one end of the pulley shait 2| projects beyond the frame It and has a suitable ,V-pulley or sheave 26 mounted thereupon.

As is clearly shown in Figs. 1 and 4, a directcurrent magnet 21, of any suitable construction,

" is disposed between the upper and lowerv flights of the belt |8and is supported upon a suitable transverse block 28 and planks or members 28,

For supporting the magnetic elements. 38, a flat plate 31 is-adiustablyconnected to the beams l2 and said elements depend from and are secured tothe plate. A plurality of vertical, depending legs or straps 38, having longitudinal slots 39 formed therein as shown in Fig. 1, project upwardly from the plate 31 along the external.

lateral surfaces of the beams I2 and the slots y of the straps receive bolts 40 which have wing and secured to the beams I 5. This direct-current magnet is for the purpose of magnetizing the particles of the ore, or other material to be separated, and maximum activity is attained if said magnet is of sufficient strength to completely saturate said particles. A field strength of approximately 2700 oersteds is usually required in order to obtain complete saturation. Of course,

although the use of a direct-current magnet is preferable, the same may be omitted in the event that the ore or other material is previously magnetized or possesses sufiicient magnetism.

An alternating-current magnet 3| is also disposed between the flights of the feed belt |8 inter-- mediate the nonmagnetic pulley and the directcurrent magnet 21, being supported upon a plate or platform 32 which is spaced above and secured to the beams l5 by a plurality of upright legs 33. As is clearly shown in Fig. 2, themagnet 3| pref erably consists of a plurality of small individual magnetic elements 34 which are disposed in transverse, parallel rows at the central portion of the belt and these magnetic elements are secured to the plate 32 in the usual manner. Although the upper ends of the elements 34 are contiguous to the upper flight of the belt 18, this distance and the magnetic strength of the field created by said elements is such that the field strength is not in excess of the coercive force of the particles carried by said belt. However, this strength or intensity is sufficiently close to such coercive force to activate and repel the particles, whereby the An attracting, alternating-current, magnet 35 depends from the beams l2 so as to be disposed above a portion of the belt H3 and its nonmagnetic pulley 26, and preferably consists of a plurality of individual magnet elements 36 arranged in transverse, parallel rows. It has been foundthat the magnetic elements are more effective than a single magnet and said elements as well as the rows thereof are preferably positioned in close proximity to one another, as is clearly shown in Figs. 2, 3 and 4; However, if desired, the rows may be spaced some distance apart so that each individual row will act independently and thereby increase the capacityof the magnet. Of course, this spacing should not be of suficient distance to create a zone of weak magnetic intensity between adjacent elements. Although not illustrated, the individual magnet elements or the rows '-thereof may be ofiset relative to each other so as to force the concentrates attracted by said elements through a tortuous or circuituous path or be dropped and picked up again, as will hereinafter be more fully explained.

nuts 4| screw-threaded upon the outer ends thereof. longitudinally-extending, horizontal slots 42 are formed in the beams |2 for receiving the bolts '40, whereby the plate 31 and its attached magnetic elements may be adjusted hori zontally as well as vertically of the frame l0 and belt I 8. Manifestly, the vertical adjustment permits the effective intensity of the magnet 35 to be varied, while the horizontal or longitudinal adjustment makes it possible for more or less of said magnet to overlie or project beyond the end of the feed belt I8 and its pulley 20. As is clearly shown in Fig. 3, the plate 31 is of substantially the same width as the frame l0 so as to be readily suspended from the beams I2. However, each transverse row of magnetic elements 38 is of a length less. than the width of the feed belt so as to be confined within the longitudinal margins thereof. v

An endless conveyor belt 43 is supported by the beams |2 with its upper flight preferably above the plate and its lower flight underlying the magnetic elements and overlying the feed belt. The belt 43, which will be hereinafter referredto as the concentrate belt,.is carried by means of a pair of spaced pulleys 44, each pulleyhaving its shaft 45 journaled within suitable brackets or bearing blocks 46which depend from the underside of adjustments of the pulleys 44 and the concentrate belt 43. One of the latter pulleys is disposed forwardly of the attracting magnet 35 ad'- jacent the forward end of the frame, while the 8 other pulley is positioned in a vertical plane substantially intermediate the direct-current magnet 21 and the repulsion magnet 3| and rearwardly of said attracting magnet. As is clearly shown in Fig. 2, one end of the shaft 45 of this rearwardlydisposed pulley 44 projects beyond the frame ill and has a suitable V-pulley or sheave 5| mounted on the outer end thereof.

By means of the pulley 5|, the conzentrate belt is drivenin a counter-clockwise direction whereby the lower flight thereof travels in the same direction as the upper flight oi the feed belt W or toward the forward end of the frame. The belts may be driven by the same means (not shown) at the same rate of speed or at different rates of speed. In the later event, it is usually preferable for the concentrate belt to travel at a faster rate so as to permit more rapid removal of the concentrate. For the most effecive separation of the magnetic particles from the tailings, the strength of the magnetic elements 36 is less than the coercive force of the magnetic particles and this strength may be varied so as to provide a gradual or tapered pick-up and release wlth an intermediate zone or plateau of maximumintensity. Thus, there is less entrainment of tailings during the pick-up of the mag netic particles by the attracting magnet 35. By tapering the strength of this magnet, or its magnetic elements, toward its forward end, middlings may be separated from the concentrate by drainage. The zone or plateau of maximum intensity is preferably'located substantially in alinement with the non-magnetic pulley 20 of the feed belt so as to extend a slight distance beyond either side of said pulley and particularly beyond the forward end of said belt. v

Improved results are obtained by the use of a rake or agitating member 52, of wood or other non-magnetic material, which depends from the plate 31 a slight distance rearwardly of the shaft 24 of the pulley 20 and above the belt I8. As is clearly shown in Fig. 5, a plurality of short prongs or teeth 53 are secured to the undersurface of the rake 52 so as to engage the material carried by the feed belt when said rake is properly positioned intermediate said feed belt and the concentrate belt. Manifestly, engagement of the prongs 53 with material supported by the feed belt stirs up or agitates the same so as to expose the lower or underportion of said material, whereby a somewhat thicker bed or stream of material may be employed. A plurality of hoppers 54, 55 and 55 are supported between the beams I 5, below the concentrate belt and forwardly of the feed belt, and have intermediate adjustable vanes 51 and 58 at their upper ends. These hoppers are of conventional construction and the rearwardmost hopper 54 has an enlarged, open upper end for receiving a portion of the feed belt and its pulley 20 whereby the gangue or inactive tailings .will drop directly into said hopper from said belt. The intermediate hopper 55 receives the middlings and is preferably disposed beneath a portion of the attracting magnet 35 which is of decreasing intensity, while the forwardmost hopper 56 projects beyond said magnet so as to receive the concentrates as they drop from the concentrate belt.

In carrying out the method, the dry ore, or other material to be separated, is reduced in size to give the desired degree of liberation and, if necessary, is properly converted, byreduction and/or oxidation, to substance having a sufliciently high coercive force and remanence. This material is fed uniformly to the feed belt l8 by the hopper l6 and is conducted by said belt to the field of the direct current magnet 21 in a relatively thin bed or stream. After being magnetized, which magnetization may be performed before the material is fed to the belt, said material travels into the field of the alternatingcurrent repulsion magnet 3| and the material becomes very active due to the magnetization thereof or its inherent magnetism. A separation of the active concentrates and inactive tailings is accomplished by the agitation or vertical motion of the magnetic particles. Since these magnetic particles have a coercive force of greater strength than the intensity of the magnetic field, said field is of insufi'lcient strength to demagnetize said particles and the same are repelled by the changing alternating-current. Actually, the particles are attracted and repelled alternately, but the attraction is ineffective because of the supporting surface afforded by the feed belt. Since the magnetic particles retain their polarity, the repelled poles of said particles will cause the same to jump or move upwardly and the repulsion is effective. This activity or agitation of the magnetic particles continues until the material moves out of the field of the magnet 3!.

The material is then conducted into the field of the alternating-current, attracting magnet 35 and its magnetic elements 36, wherein the activity of the particles is relatively complex. Upon entering this magnetic 'field and while still carried by the feed belt, the magnetic particles behave or 'react in much the same manner as when the same were under the influence 0f the magnet 3|. This is in part due to the lower strength of the initial portion of the attracting magnetic field, or that portion of said magnetic field which is disposed rearwardly of the pulley 20, as well as the distance of the material from the magnet 35. However, the intensity of this magnetic field may exceed the coercive force of some of the magnetic particles so as to be sufficient to attract to and hold the same in engagement with the concentrate belt 43.

If the intensity of the magnet 35 is properly adjusted, either as to distance or ampere-turns, the strength or intensity of the field will not exceed the coercive force of most of the particles. The latter will retain their individual polarity and will continue to adjust themselves by motion to the alternating magnetic field so as to be acted upon by both attracting and repelling magnetic forces. Upon being repelled, the particles leave the surface of the concentrate belt and this movement will be aided by gravity, said particles again being attracted upon changing of the field. In effect, the particles are in a state of suspension and the same are carried by the underside of the concentrate belt in a tenuous active mass.

Upon reaching the zone or plateau of maximum intensity, substantially all of the magnetic particles will be so held. The particles held in engagement with the concentrate belt are not inactive as the same will be agitated by the bom- 45 bardment of more'active particles and said particles will themselves become more active due to a lag in magnetization which prevents a complete change of polarity of the particles.

This reduces to a minimum the entrainment of gangue. The majority of the particles are attracted more or less vertically, but will move horizontally relative to the belt to zones of denser intensity along the edges of the magnetic elements 36 or the rows thereof and, due to this horizontal travel, additional gangue drains out.

As the material, being carried along by the concentrate belt, passes from the zone of maximum intensity through the forward end zone of decreasing magnetic intensity, middlings composed of particles of locked grains and of lower remanence than the other particles drop out and are caught by the hopper 55. This material may be reground to a. finer size and again passed through the separator to recover additional magas to force the concentrates carried by the beltseparation of iron ores, other minerals containstantially all free gangue is eliminated from the concentrates by the separating method and apparatus set forth herein. The most important limitation inherent in direct-current magnetic 2. The method of magnetically separating a mixture of materials certain particles of which have magnetic properties and others of which have non-magnetic properties which includes,-

passing the mixture above an alternating current magnetic field of a strength less than the coercive force of the particles having magnetic properties so as to cause at least a partial stratification of said mixture, and then passing said materials below a second alternating current magnetic field of a strength greater than the coercive force of some of the particles having magnetic properties and not greater than the coercive force of most of the magnetic particles so as to separate the magnetic particles from said nonmagnetic particles.

3. An apparatus for magnetically separating materials having particles with magnetic and separators has been effectively overcome and,

at the same time, the activit of an alternatingcurrent field has been more efliciently utilized so as to obtain higher-grade concentrates and increased recovery as well as increased capacity.

The foregoing description of the invention is explanatory thereof and various changes in the 1 size, shape and materials, as well as in the details of the illustrated construction may be made, within the scope ofthe appended claims, without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is:

1. The method of magnetically separating a mixture of materials certain particles of which have magnetic properties and other of which have non-magnetic properties. which consists in passing said mixture through a direct current magnetic field so as to impart to or to increase the coercive force of the particles having magnetic properties. then passing all of said mixture above an alternating current magnetic field of a stren th less than the coercive force of the particles having magnetic properties so as to cause at least a partial stratification of the said mixture. and finally passing said materials below a second alternating current magnetic field of progressively increasing and diminishing force, the force of said second alternating current magnetic field being greater than the coercive force of some of the particles havingmagnetic properties and not greater than the coercive force of most of the magnetic particles, whereby to separate the latter from said particles of non magnetic force.

non-magnetic properties including, a material feed hopper, a conveyor disposed beneath the feed hopper, a first alternating current magnet disposed between the upper and lower runs. of the conveyor and having a maximum intensity less than the coercive force of the particles having magnetic properties, a second conveyor disposed above and parallel to the first named conveyor in overlapping relation to the latter and to the first named alternating current magnet, and a second. alternating current magnet disposed between the upper and lower runs of the second named conveyor having a maximum intensity greater than the coercive force of some of the magnetic particles and not greater than the coercive force of most of the magnetic particles.

4. Anapparatus for magnetically separating materials in accordance with claim 3, whereinthe second alternating current magnet is constructed so as to-produce an alternating magnetic field of gradually increasing and diminishing zones of intensity.

ARTHUR B. DRESCHER.

REFERENCES CITED The following references are of record in the file of this patent:

Number UNITED STATES PATENTS OTHER REFERENCES R. I. 3268, Bureau of Mines, Feb. 1935, pages 101-107. Copv found in Scientific Library.

Magnetic Separation of Ores, Bulletin 425,

Bureau of Mines, pages 271-273 and pages 109- 

